Patterns defined by the DrawingBrush expand to fill the area of the rectangle

   
 

<Window x:Class="Workspace.DockExample"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Workspace" Width="640" Height="480">
          <Rectangle Width="100" Height="100" Stroke="Black" StrokeThickness="1">
            <Rectangle.Fill>
              <DrawingBrush>
                <DrawingBrush.Drawing>
                  <GeometryDrawing Brush="MediumBlue">
                    <GeometryDrawing.Geometry>
                      <GeometryGroup>
                        <EllipseGeometry RadiusX="0.2" RadiusY="0.45" Center="0.5,0.5" />
                        <EllipseGeometry RadiusX="0.45" RadiusY="0.2" Center="0.5,0.5" />
                      </GeometryGroup>
                    </GeometryDrawing.Geometry>
                    <GeometryDrawing.Pen>
                      <Pen Thickness="0.1" Brush="Black" />
                    </GeometryDrawing.Pen>
                  </GeometryDrawing>
                </DrawingBrush.Drawing>
              </DrawingBrush>
            </Rectangle.Fill>
          </Rectangle>

</Window>